This invention relates generally to an improved clutch brake unit for use in conjunction with a clutch assembly for retarding the motion of the driven clutch shaft when the clutch is released and which, more importantly, limits the amount of torque that can be applied to the shaft through the unit.
Clutch brake units for use in clutch assemblies and, in particular, heavy duty clutch assemblies, are well known in the art. In practice, the clutch brake is designed to be actuated through the clutch pedal mechanism of the vehicle. Typically, upon depressing the pedal, the clutch is disengaged thereby releasing the driven shaft that is operatively connected to the transmission. As a consequence, the shaft ordinarily will continue to rotate at relatively high speeds, or at least at speeds which make the shifting of gears difficult. The clutch brake is usually actuated by further depressing the clutch pedal which, in turn, causes a braking torque to be applied to the driven shaft to retard or stop its motion.
Conventionally, the clutch brake unit is keyed or splined to the shaft and the braking load transmitted through a friction coupling that is designed to limit the load that can be applied to the shaft. The friction coupling thus provides a safety feature which considerably reduces the possibility of damaging the brake linkage. One such unit is disclosed by Sink in U.S. Pat. No. 3,763,977 wherein a pair of Belleville washers are utilized in the friction coupling as the load limiting components in the system. As such, the washers form an integral part of the torque transmitting linkage and are thus subjected to excessive wear which can lead to premature failure of the unit.